In my procedures historically, I've always caught an exception, then raised it after a ROLLBACK. I see in MSDN that the recommended approach (for SQL2012+) is to THROW.
Based on this example procedure:
CREATE PROC my_procName
#id int
AS
BEGIN TRY
BEGIN TRAN
UPDATE [tbl_A] WHERE (ID=#id);
UPDATE [tbl_B] WHERE (fkID=#id);
UPDATE [tbl_C] WHERE (fkID=#id);
COMMIT TRAN
END TRY
BEGIN CATCH
ROLLBACK TRAN
DECLARE #ErrMsg nvarchar(4000)
DECLARE #ErrSeverity int
SET #ErrMsg = ERROR_MESSAGE()
SET #ErrSeverity = ERROR_SEVERITY()
RAISERROR(#ErrMsg, #ErrSeverity, 1)
END CATCH
GO
Is this the correct way to throw the exception, while preserving the ROLLBACK?
CREATE PROC my_procName
#id int
AS
BEGIN TRY
BEGIN TRAN
UPDATE [tbl_A] WHERE (ID=#id);
UPDATE [tbl_B] WHERE (fkID=#id);
UPDATE [tbl_C] WHERE (fkID=#id);
COMMIT TRAN
END TRY
BEGIN CATCH
ROLLBACK TRAN
THROW
END CATCH
GO
I have already looked at MSDN, Google, and this site for examples, but none include the ROLLBACK, so this is just a quick question to make absolutely sure.
Just for the record statement before THROW statement should be terminated by semicolon. But generally your approach is correct - THROW ends the batch therefore must be the last statement you want to execute in your catch block. Optionally you can use THROW with parameters:
THROW [ { error_number | #local_variable },
{ message | #local_variable },
{ state | #local_variable } ]
[ ; ]
Related
ALTER PROCEDURE Add_Edit_Courses_new
#CourseCode VARCHAR,
... other params ...
AS
BEGIN TRY
DECLARE #ErrorCode INT =0, #ErrorMessage VARCHAR(25) = 'Action failed'
IF #TaskType > 2
BEGIN
RAISERROR('Wrong action key',16,1)
END
ELSE
BEGIN TRANSACTION
BEGIN
DECLARE #message VARCHAR(MAX)
IF #TaskType = 1
BEGIN
INSERT INTO Courses(...) VALUES(#CourseCode,...)
SET #message = 'Added Successfully'
END
ELSE IF #TaskType = 2
BEGIN
UPDATE Courses SET CourseCode=#CourseCode,...;
SET #message = 'Modified Successfully'
END
END
COMMIT TRANSACTION
END TRY
BEGIN CATCH
ROLLBACK TRANSACTION
SELECT ERROR_NUMBER() AS ErrorNumber, ...
END CATCH
I wrote this stored procedure to insert and update and I used (1 & 2) to differentiate the task while using a try and catch, but every time I try to execute this stored procedure I keep getting that error, please can you help me with where I am wrong, I am just learning this principle for the first time.
Why is BEGIN TRANSACTION before BEGIN? I feel like BEGIN TRANSACTION/COMMIT TRANSACTION should be inside the ELSE conditional. With some noise removed:
IF #TaskType > 2
BEGIN
RAISERROR('Wrong action key',16,1);
END
ELSE
BEGIN -- moved this here
BEGIN TRANSACTION;
-- BEGIN -- removed this
DECLARE #message varchar(max);
IF #TaskType = 1
BEGIN
INSERT INTO Courses(...
SET #message = 'Added Successfully';
END
IF #TaskType = 2 -- don't really need ELSE there
BEGIN
UPDATE Courses SET ...
SET #message = 'Modified Successfully';
END
-- END -- removed this
COMMIT TRANSACTION;
SELECT #message;
END -- moved this here
In your catch you just blindly say:
ROLLBACK TRANSACTION;
This should be updated to:
IF ##TRANCOUNT > 0
BEGIN
ROLLBACK TRANSACTION;
END
Note that if you have a conditional where multiple statements are not wrapped correctly in BEGIN / END, they won't execute like you think. Consider:
IF 1 = 0
PRINT 'foo';
PRINT 'bar';
You get bar output every time, regardless of the result of the conditional.
You had something similar:
IF 1 = 1
-- do stuff
ELSE
BEGIN TRANSACTION;
BEGIN
-- do stuff
END
COMMIT TRANSACTION;
In that case, -- do stuff and the commit happened every time, even if the begin transaction did not, because that BEGIN/END wrapper (and anything that followed it) was not associated with the ELSE.
Perhaps a little dry and wordy if you're new to the topic, but Erland Sommarskog has a very comprehensive series on error handling here, might be worth a bookmark:
https://www.sommarskog.se/error_handling/Part1.html
https://www.sommarskog.se/error_handling/Part2.html
https://www.sommarskog.se/error_handling/Part3.html
Imo there are some major issues with this code. First, if the intention is for the transaction to be atomic then SET XACT_ABORT ON should be specified. Per the Docs RAISERROR does not honor SET XACT_ABORT ON so it could be converted to use THROW. Second, in cases where the ELSE block in the code is hit then COMMIT will always be hit (regardless of what happens to the commitable state of the transaction).
Also, the code performs the ROLLBACK before the code:
SELECT ERROR_NUMBER() AS ErrorNumber, ...
It's the ROLLBACK which clears the error messages and returns the state to normal. To catch the error metadata SELECT it before the ROLLBACK happens.
We have a data import system where we are processing CSV files, each file contains a set of records that have to be validated and processed individually. If they fail for some reason, they're marked with the error and we then go on to the next record. They can fail for either logical or database errors such as dup key or foreign key errors.
The stored procedure that processes the data is either called from a client application, or from an agent job. The difference is that the app will create a transaction whereas the job will not before calling the proc.
SET NOCOUNT ON;
SET XACT_ABORT OFF;
DECLARE #trancount_in INT,
#xstate INT,
#Row INT,
#MaxRows INT
SET #trancount_in = ##trancount
-- CODE: import data into temp table
select #Row = 1,
#MaxRows = ##Rowcount
IF #transcount_in = 0
BEGIN TRANSACTION
while #Row <= #MaxRows
-- CODE: Get data record from table
begin try
save transaction myproc
-- CODE: validate and process record
end try
begin catch
SELECT #xstate = XACT_STATE()
IF #xstate = -1 BEGIN
ROLLBACK
Raiserror('error',16,1)
END
IF #xstate = 1 and ##Trancount = 0 BEGIN
ROLLBACK
Raiserror('error',16,1)
END
IF #xstate = 1 and ##Trancount > 0
ROLLBACK TRANSACTION myproc
-- CODE: update import record with error here
end catch
set #Row = #Row + 1
End
IF #transcount_in = 0
COMMIT
So fairly simple so far, but looking at lots of documentation, it says that you should check the xact_state for -1 in the catch block, but I don't want the transaction to fail at this point. I just want to go on to the next row in the import. So if xact_abort is off, would we ever get the xact_state of -1 in the catch block?
I know that the catch doesn't actually catch all errors, but I have found out that if you create a parent proc with a try catch block then it will catch more errors than the block in the actual proc. So I will be moving the loop logic to a parent proc and then just do the processing in the current one.
Is there anything else I should be doing to mitigate any errors that might occur?
Hope this isn't too confusing.
Cheers
Adrian
The question should be quite simple, but I can't figure out the answer nor why my stored procedure is not working.
CREATE PROCEDURE spTest_Delete
#ID int
AS
begin tran
declare #err int
declare #errMesage nvarchar(max)
set #errMesage = ''
set #err = 0
delete from Test
where ID = #ID
set #err = ##ERROR
set #errMesage = ERROR_MESSAGE()
if #err = 0
commit tran
else
begin
RAISERROR(N'Could not delete !Error nr: %d. Message: %s', 1, 16, #err, #errMesage)
rollback tran
end
This procedure runs ok, but in case of FK constraint on the delete statement it runs into an error (which is good) and I would like to catch the error.
Msg 547, Level 16, State 0, Procedure spTest_Delete, Line 12
The DELETE statement conflicted with the REFERENCE constraint
"FK_TEstFK_Test". The conflict occurred in database "Test", table
"dbo.Test", column 'ID'. The statement has been terminated.
Could not delete!
Error nr: 547. Message: (null) Msg 50000, Level 1, State 16
I always get null for my message variable, even though the delete statement throws an error.
You might want to start using TRY..CATCH block in your procedures
Implements error handling for Transact-SQL that is similar to the
exception handling in the Microsoft Visual C# and Microsoft Visual C++
languages. A group of Transact-SQL statements can be enclosed in a TRY
block. If an error occurs in the TRY block, control is passed to
another group of statements that is enclosed in a CATCH block.
So your procedure could be rewritten as:
CREATE PROCEDURE spTest_Delete #ID INT
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRY
BEGIN TRANSACTION
DELETE
FROM Test
WHERE ID = #ID;
COMMIT TRANSACTION
END TRY
BEGIN CATCH
IF ##TRANCOUNT > 0
ROLLBACK TRANSACTION
SELECT ERROR_NUMBER(), ERROR_MESSAGE();
END CATCH
END
Also, please note that you're running as single delete statement. It means that it doesn't need to be wrapped up in a transaction. This question explains why.
Your code becomes this:
CREATE PROCEDURE spTest_Delete #ID INT
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRY
DELETE
FROM Test
WHERE ID = #ID;
END TRY
BEGIN CATCH
SELECT ERROR_NUMBER(), ERROR_MESSAGE();
END CATCH
END
Now why your #errMessage is always NULL? Because ERROR_MESSAGE() is valid ONLY IN CATCH BLOCK. That's written in documentation:
Returns the message text of the error that caused the CATCH block of a
TRY…CATCH construct to be run.
Using TRY..CATCH in Transact-SQL tells this:
Error information is retrieved by using these functions from anywhere
in the scope of the CATCH block of a TRY…CATCH construct. The error
functions will return NULL if called outside the scope of a CATCH
block.
Try to use TRY CATCH and catch your error like this:
BEGIN TRY
delete from Test
where ID = #ID
END TRY
BEGIN CATCH
SET #ErrorMessage = ERROR_MESSAGE()
SET #ErrorSeverity = ERROR_SEVERITY()
SET #ErrorState = ERROR_STATE()
RAISERROR(#ErrorMessage, #ErrorSeverity, #ErrorState)
BREAK
END CATCH
In Sql Server 2008 R2, I am creating a procedure with multiple transactions in it. Try..Catch Block is used for each transaction. I use output parameter to catch the error code and message since it will be caught by the main program. But When there is errors the output parameter are not correct set to the error message and code, what is problem here?
create procedure xxx (#P_Return_Status VARCHAR(1) OUTPUT, #P_Error_Code INT OUTPUT,)
AS
BEGIN
BEGIN TRY
BEGIN TRANSACTION TR1
.....
COMMIT TRANSACTIOn TR1
END TRY
BEGIN CATCH
IF (##TRANCOUNT > 0)
BEGIN
ROLLBACK TRANSACTION TR1
END
Set #P_Error_Code = Error_Number();
Set #P_Error_Messages = LEFT(ERROR_MESSAGE (), 2000)
END CATCH
BEGIN TRY
BEGIN TRANSACTION TR2
.....
COMMIT TRANSACTIOn TR2
END TRY
BEGIN CATCH
IF (##TRANCOUNT > 0)
BEGIN
ROLLBACK TRANSACTION TR2
END
Set #P_Error_Code = Error_Number();
Set #P_Error_Messages = LEFT(ERROR_MESSAGE (), 2000)
END CATCH
END
GO
Any help would be really appreciated!
I just don't see the point of putting two transaction inside this one procedure, just put all of the statements in one transaction and commit it or rollback it.
if it does need to be in separate transactions put these both try...catch in two separate procedures and call one sp from another sp's try block.
create procedure xxx
#P_Return_Status INT OUTPUT
,#P_Error_Code INT OUTPUT
,#P_Error_Messages VARCHAR(2000) OUTPUT
AS
BEGIN
BEGIN TRY
BEGIN TRANSACTION TR1
/* put statements from both transaction here
or
statements for TR1
AND
call the procedure containing code for TR2
*/
COMMIT TRANSACTIOn TR1
SET #P_Return_Status = 1;
END TRY
BEGIN CATCH
IF (##TRANCOUNT > 0)
BEGIN
ROLLBACK TRANSACTION TR1
END
Set #P_Error_Code = Error_Number();
Set #P_Error_Messages = LEFT(ERROR_MESSAGE (), 2000)
SET #P_Return_Status = 0;
END CATCH
END
GO
Do u think there is a better way to write a transaction in t-sql? Is there a better approach that improves maintainability and performance of the application that uses this transaction?
-- Description: Insert email Receiver under specified subject
-- =============================================
ALTER PROCEDURE [Contact].[Receiver_stpInsert]
#First_Name nvarchar(30),
#Last_Name nvarchar(30),
#Email varchar(60),
#Subject_Id int
AS
BEGIN
SET NOCOUNT ON;
DECLARE #error_num int;
BEGIN TRANSACTION
INSERT INTO Contact.Receiver(First_Name, Last_Name, Email) VALUES(#First_Name, #Last_Name, #Email);
SET #error_num = ##ERROR;
IF (#error_num <> 0)
BEGIN
ROLLBACK;
RETURN;
END
DECLARE #rec_record_id int;
SET #rec_record_id = (SELECT Record_Id FROM Contact.Receiver WHERE Email = #Email);
SET #error_num = ##ERROR;
IF (#error_num <> 0)
BEGIN
ROLLBACK;
RETURN;
END
INSERT INTO Contact.Receiver_Subject(Receiver_Id, Subject_Id) VALUES(#rec_record_id, #Subject_Id);
SET #error_num = ##ERROR;
IF (#error_num <> 0)
BEGIN
ROLLBACK;
RETURN;
END
SET #error_num = ##ERROR;
IF (#error_num <> 0)
BEGIN
ROLLBACK;
RETURN;
END
ELSE
BEGIN
Commit;
END
END
If you're using SQL 2005 or later, you can use the TRY...CATCH block, like this:
BEGIN TRY
BEGIN TRANSACTION;
INSERT INTO Contact.Receiver(First_Name, Last_Name, Email) VALUES (#First_Name, #Last_Name, #Email);
... other inserts etc
...
COMMIT TRANSACTION;
END TRY
BEGIN CATCH
IF ##TRANCOUNT > 0
ROLLBACK TRANSACTION;
END CATCH;
This way, you don't keep repeating the same blocks of code checking ##ERROR. If you want to know what error occurred, in the BEGIN CATCH block you can get various bits of info:
ERROR_NUMBER() returns the number of the error.
ERROR_SEVERITY() returns the severity.
ERROR_STATE() returns the error state number.
ERROR_PROCEDURE() returns the name of the stored procedure or trigger
where the error occurred.
ERROR_LINE() returns the line number inside the routine that caused the
error.
ERROR_MESSAGE() returns the complete text of the error message. The text
includes the values supplied for any
substitutable parameters, such as
lengths, object names, or times.
For a long time now I've been advocating the use of TRY/CATCH and nested transactions in stored procedures.
This pattern gives you not only the much simplified error handling of the TRY/CATCH block compared with the ##ERROR check, but it also gives all-or-nothing nested semantics for procedure invocations.
If the procedure is called on the context of a transaction then the procedure rolls back only its own changes and leaves the caller to decide whether to rollback the embedding transaction or to try an alternate error path.
create procedure [usp_my_procedure_name]
as
begin
set nocount on;
declare #trancount int;
set #trancount = ##trancount;
begin try
if #trancount = 0
begin transaction
else
save transaction usp_my_procedure_name;
-- Do the actual work here
lbexit:
if #trancount = 0
commit;
end try
begin catch
declare #error int, #message varchar(4000), #xstate int;
select #error = ERROR_NUMBER(), #message = ERROR_MESSAGE(), #xstate = XACT_STATE();
if #xstate = -1
rollback;
if #xstate = 1 and #trancount = 0
rollback
if #xstate = 1 and #trancount > 0
rollback transaction usp_my_procedure_name;
raiserror ('usp_my_procedure_name: %d: %s', 16, 1, #error, #message) ;
return;
end catch
end
The draw backs of this approach are:
It does not work with distributed transactions. Because transaction savepoints are incompatible with distributed transactions, you cannot use this pattern when distributed transactions are required. IMHO distributed transactions are evil and should never be used anyway.
It alters the original error. This problem is inherent in TRY/CATCH blocks and there is nothing you can do about it. An application that is prepared to deal with the original SQL Server error codes (like 1202, 1205, 2627 etc) will have to be changed to deal with the error codes in the above 50000 range raised by Transact-SQL code that uses TRY/CATCH.
Also a word of caution about the use of SET XACT_ABORT ON. This setting will cause a batch to abort a transaction at any error. That raises any TRY/CATCH transaction handling basically useless and I recommend to be avoided.
If you have SQL Server 2000 or before, then yes - checking the ##ERROR value is basically all you can do.
With SQL Server 2005, Microsoft introduced the TRY...CATCH construct which makes it a lot easier:
BEGIN TRY
......
-- your T-SQL code here
......
END TRY
BEGIN CATCH
SELECT
ERROR_NUMBER() AS ErrorNumber,
ERROR_SEVERITY() AS ErrorSeverity,
ERROR_STATE() AS ErrorState,
ERROR_PROCEDURE() AS ErrorProcedure,
ERROR_LINE() AS ErrorLine,
ERROR_MESSAGE() AS ErrorMessage
-- do other steps, if you want
END CATCH
Asked not long ago. My answer with a TRY/CATCH template
If you are using sql 2005 or higher you should consider the TRY CATCH approach
You can wrap it all in a try catch, and then you only need to code the rollback in one place. See this for more details.